364 MOTIONS OF INSECTS. 
them to see readily and seize the insects that fall upon the 
water, which are their prey. Sigara, however, a cognate 
genus separated from Notonecta by Fabricius, swims in 
the ordinary way. As the Gyrini are usually in motion 
at the surface, whirling round and round in circles, it is 
probable that their legs are best adapted to this move- 
ment. They dive down, however, with great ease and 
velocity when alarmed. The common water-bug (Gerris 
lacustris, Latr.), though it never goes under water, will 
sometimes swim upon the surface, which it does by 
strokes of the intermediate and posterior legs*. ‘These, 
however, are neither fringed nor dilated, but very long 
and slender, with claws, not easily detected, situated un- 
der the apex of the last joint of the foot, which covers 
and conceals them. The underside of their body—as is 
the case with Elophorus, F., and many other aquatic in- 
sects—is clothed with a thick coat of gray hairs like satin, 
which in certain lights have no small degree of lustre, 
and protect its body from the effects of the water. Some 
insects, that are not naturally aquatic, if they fall into 
the water will swim very well. I once saw a kind of 
grasshopper (Acrydium, F.), which by the powerful 
strokes of its hind legs pushed itself across a stream with 
great rapidity. 
Other insects wali, as it were, in the water, moving 
their legs much in the same way as they would do on 
the land. Many smaller species of water-beetles, belong- 
ing to the genera Hydrophilus, Hlophorus, Hydrena, 
Parnus, Elmis, &c., thus win their way in the waves.— 
Thus also the water-scorpion (Nepa) pursues its prey ; 
and the little water-mites (Hydrachna) may be seen in 
2 De Geer, iil, 314. 
